This application seeks support for a project of research directed toward better understanding of the molecular mechanisms and cellular functions of chloride transport across human red blood cell membranes. Our investigation of the molecular mechanism of anion transport seeks to solve four major unsolved problems: First, the identification of the components of the erythrocyte membrane responsible for and controlling chloride transport; second, the mechanisms by which these components may be reincorporated into model lipid membrane systems; third, the factors involved in the kinetic behavior of these reconstituted anion transport systems; fourth, the electrical properties of the anion exchange system to determine whether exchange and conductance are mediated by a common mechanism. Experiments designed to answer questions relevant to these problems involve observations under various conditions of solubilization and separation of membrane proteins, electrical properties of thin lipid bilayer, fluxes of tracer ions across red cells and bilayer membranes.